Cracking, water permeability and deformation of compacted clay liners improved by straw fiber

Abstract

The cracking resistance performance, impermeability, strength and deformation characteristics of improved clay were systematically evaluated by cracking test, water permeability test, unconfined compression test and shear test, respectively. The cracking test suggested a high resistance of the improved clay by straw fiber against cracking. With the increase of fiber content (FC), the cracking intensity factor (CIF) i.e. the ratio of the crack area to the total area, decreased at low fiber contents and then turned to increase at higher fiber contents. However, the effect of fiber additive on the surface shrinkage was not significant. The improved clay with FC=0.3% was found to have the highest resistance to cracking. After 25days of desiccation, CIF and surface shrinkage of compacted clay were determined to be 0.015 and 12.1% respectively. However, CIF of the improved clay with FC=0.3% was only 0.0013 and surface shrinkage was 10.31%. Cracking was propagated by wetting–drying cycles. After four wetting–drying cycles, the CIF of the compacted clay was 0.032 and the CIF of the improved clay with FC=0.3% was 0.0081. The result of water permeability test for cracked clay indicated that a traditional landfill cover system merely consisting of compacted clay would not be sufficient to serve as an effective barrier against rainwater permeation into the landfill. At a rainfall intensity of 10mm/d, the rainwater penetrated to a 15cm depth of the clay liners. The improved clay with FC=0.3% had the least permeability. The rainwater had not penetrated to the 15cm depth of clay liners even if the rainfall intensity reached 50mm/d. The results of unconfined compression tests and shear tests indicated that with the increase of FC, the unconfined compressive strength and shear strength increased firstly and then decreased. At FC=0.3%, the unconfined compressive strength peaked at 459.15kPa, and c, φ peaked at 80.9kPa and 21.06°, respectively. The improved clay with straw fiber additive could be used in landfill cover system to enhance the anti-seepage ability and strength of landfill liners.